The present state of the art in cooling techniques uses turbulent flow macro-channel exchangers. Present heat exchangers use fin spacing which is large with poor thermal transfer to coolant efficiency. Additionally, in cooling a heat source, the heat source is often separated from the heat exchanger by several thermal interfaces or is separated by poor thermally conductive materials such as thermal grease which results in poor heat transfer.
An important physical problem in computer systems is that of heat dissipation and removal. The heat generated by a single logic gate is small: at most a few milliwatts for most high-speed logic such as ECL (emitter coupled logic) and is much less for other logic families such as CMOS (complementary metal oxide semiconductors). However, when VSLI (very large scale integrated circuit) systems are fabricated with tens or hundreds of thousands of gates on a single chip, the total power consumption could conceivably reach the kilowatt level if high-performance logic is used. Even if a low-power logic family is used, a complete high-performance computer system might have 10.sup.7 to 10.sup.8 switching elements (e.g., transistors) and comprise hundreds of chips. If these chips are packed very closely together to minimize propagation delays, the problem of removing tens or (even hundreds) of kilowatts of heat while maintaining normal circuit temperatures (usually less than 120.degree. C. Preferably even lower for enhanced reliability) from a system volume of less than 1 liter becomes challenging.
It has been widely considered that such a heatremoval task is effectively impossible. One pioneer of system physics has estimated that forced-air cooling of logic chips is limited to power densities of about 1 W/cm.sup.2. and that liquid cooling is limited to about 20 W/cm.sup.2. Another leader in high-speed Josephson systems has stated that, with present technology, it would be impossible to remove 20 kW from a room-temperature computer having a volume less than 640 cm.sup.3, and that even a tenfold reduction in power to 2 kW would still present a "difficult, if not impossible" cooling task. Indeed, the best commercial technologies presently available for cooling density packed arrays of integrated circuits are the IBM Thermal Conduction Module and the Honeywell Silent Liquid Integral Cooler, both of which are limited to heat fluxes of about 20 W/cm.sup.2.
Recently, efforts at Stanford University have been toward a new direction in the optimization of thermal equations. Such a heat exchanger structure was proposed by David Bazeley Tuckerman in his University of California doctoral thesis, of February 1984, entitled "Heat-Transfer Microstructures for Integrated Circuits" UCRL-53515. Tuckerman integrated a heat exchanger into a silicon device by etching grooves in the silicon. The concept and dimensions of that heat exchanger were derived by Tuckerman in his thesis. The process developed at Stanford University used small channels etched into silicon wafers. These small channels became heat transfer fluid flow channels. Such heat exchange structures are very efficient and take up minimal space. However, the placement of the heat transfer fluid flow channel in the silicon wafer presents problems because silicon is a poor thermal conductor and is brittle, thus very susceptible to breakage. The increased stress due to grooves in the silicon substrate of integrated circuits increases the possibility for breakage and, thus, decreases the reliability of the integrated circuit, especially in a shock environment.
Products which are weight-constrained and/or space-constrained and which have significant power dissipation are likely candidates for improvements in cooling capacity and size reduction. Airborne devices, missile devices, and torpedo devices are especially sensitive to size and weight requirements making them good candidates for such improvement. Vehicle- and man-portable equipments are sensitive to weight and volume constraints, but have less emphasis on power density. Large computer and groundbased radars can benefit from improved cooling capacity and size reduction, provided the improved heat exchanger accomplishes its results at a sufficiently low cost when compared to present techniques. By using the microchannel structure of this invention for a heat exchanger, less material is required and smaller, lighter-weight cabinets and hardware can be realized.